Human

== Biology ==

=== Anatomy and physiology ===
{{Main|Human body}}
[[File:Anterior view of human female and male, with labels 2.png|thumb|upright=1.5|Basic anatomical features of female and male humans. These models have had [[body hair]] and male [[facial hair]] removed and head hair trimmed.]]
Most aspects of human physiology are closely [[Homology (biology)|homologous]] to corresponding aspects of animal physiology. The [[dental formula]] of humans is: {{DentalFormula|upper=2.1.2.3|lower=2.1.2.3}}. Humans have proportionately shorter [[palate]]s and much smaller [[Human tooth|teeth]] than other primates. They are the only primates to have short, relatively flush [[canine teeth]]. Humans have characteristically crowded teeth, with gaps from lost teeth usually closing up quickly in young individuals. Humans are gradually losing their [[wisdom teeth|third molars]], with some individuals having them congenitally absent.<ref name="Revolution">{{cite book| vauthors = Collins D |url=https://archive.org/details/humanrevolutionf0000coll|title=The Human Revolution: From Ape to Artist|year=1976|isbn=978-0-7148-1676-0|page=[https://archive.org/details/humanrevolutionf0000coll/page/208 208]|publisher=Phaidon |url-access=registration}}</ref>

Humans share with chimpanzees a [[Vestigiality|vestigial]] tail,<ref name="CNN-20240323">{{cite news |last=Weisberger |first=Mindy |title=Why don't humans have tails? Scientists find answers in an unlikely place |url=https://www.cnn.com/2024/03/23/world/humans-tails-genetic-mutation-junk-dna-scn/index.html |date=March 23, 2024 |work=[[CNN]] |url-status=live |archiveurl=https://archive.today/20240324031927/https://www.cnn.com/2024/03/23/world/humans-tails-genetic-mutation-junk-dna-scn/index.html |archivedate=March 24, 2024 |accessdate=March 24, 2024 }}</ref> [[Appendix (anatomy)|appendix]], flexible shoulder joints, grasping fingers and [[opposable thumb]]s.<ref>{{cite book| vauthors = Marks JM |title=Human Biodiversity: Genes, Race, and History|date=2001|publisher=Transaction Publishers|isbn=978-0-202-36656-2|page=16|language=en}}</ref> Humans also have a more barrel-shaped chests in contrast to the funnel shape of other apes, an adaptation for bipedal respiration.<ref>{{cite journal|last1=Gea|first1=J|year=2008|title=The Evolution of the Human Species: A Long Journey for the Respiratory System|journal=Archivos de Bronconeumología ((English Edition))|volume=44|issue=5|pages=263–270|doi=10.1016/S1579-2129(08)60042-7}}</ref> Apart from bipedalism and brain size, humans differ from chimpanzees mostly in [[smelling]], [[hearing]] and [[Digestion#Protein digestion|digesting proteins]].<ref name="O'Neil" /> While humans have a density of [[hair follicle]]s comparable to other apes, it is predominantly [[vellus hair]], most of which is so short and wispy as to be practically invisible.<ref>{{cite news|date=2017|title=How to be Human: The reason we are so scarily hairy|work=New Scientist|url=https://www.newscientist.com/article/mg23631460-700-why-are-humans-so-hairy/|access-date=29 April 2020|archive-date=25 February 2021|archive-url=https://web.archive.org/web/20210225235006/https://www.newscientist.com/article/mg23631460-700-why-are-humans-so-hairy/|url-status=live}}</ref><ref>{{cite journal | vauthors = Sandel AA | title = Brief communication: Hair density and body mass in mammals and the evolution of human hairlessness | journal = American Journal of Physical Anthropology | volume = 152 | issue = 1 | pages = 145–150 | date = September 2013 | pmid = 23900811 | doi = 10.1002/ajpa.22333 | hdl-access = free | hdl = 2027.42/99654 }}</ref> Humans have about 2 million [[sweat gland]]s spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on the palm of the hand and on the soles of the feet.<ref>{{cite web| vauthors = Kirchweger G |title=The Biology of Skin Color: Black and White|url=https://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html|url-status=live|archive-url=https://web.archive.org/web/20130216070146/https://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html|archive-date=16 February 2013|access-date=6 January 2013|date=2 February 2001|work=Evolution: Library|publisher=PBS}}</ref>

It is estimated that the worldwide average [[Human height|height for an adult human]] male is about {{Height|cm=171|precision=0}}, while the worldwide average height for adult human females is about {{Height|cm=159|precision=0}}.<ref>{{cite journal|vauthors=Roser M, Appel C, Ritchie H|date=8 October 2013|title=Human Height|url=https://ourworldindata.org/human-height|journal=Our World in Data|access-date=30 July 2022|archive-date=30 January 2021|archive-url=https://web.archive.org/web/20210130203158/https://ourworldindata.org/human-height|url-status=live}}</ref> Shrinkage of stature may begin in middle age in some individuals but tends to be typical in the extremely [[Old age|aged]].<ref>{{cite web|title=Senior Citizens Do Shrink – Just One of the Body Changes of Aging|url=https://seniorjournal.com/NEWS/Aging/5-11-28-SeniorsDoShrink.htm|url-status=dead|archive-url=https://web.archive.org/web/20130219004303/https://seniorjournal.com/NEWS/Aging/5-11-28-SeniorsDoShrink.htm|archive-date=19 February 2013|access-date=6 January 2013|work=News|publisher=Senior Journal}}</ref> Throughout history, human populations have universally become taller, probably as a consequence of better nutrition, healthcare, and living conditions.<ref>{{cite journal | vauthors = Bogin B, Rios L | title = Rapid morphological change in living humans: implications for modern human origins | journal = Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology | volume = 136 | issue = 1 | pages = 71–84 | date = September 2003 | pmid = 14527631 | doi = 10.1016/S1095-6433(02)00294-5 }}</ref> The average [[Body weight|mass]] of an adult human is {{Convert|59|kg|lb|abbr=on}} for females and {{Convert|77|kg|lb|abbr=on}} for males.<ref>{{cite web|title=Human weight|url=https://www.articleworld.org/index.php/Human_weight|url-status=live|archive-url=https://web.archive.org/web/20111208053451/https://articleworld.org/index.php/Human_weight|archive-date=8 December 2011|access-date=10 December 2011|publisher=Articleworld.org}}</ref><ref>{{cite web | vauthors = Schlessingerman A | date = 2003 |title=Mass Of An Adult|url=https://hypertextbook.com/facts/2003/AlexSchlessingerman.shtml|url-status=live|archive-url=https://web.archive.org/web/20180101030223/https://hypertextbook.com/facts/2003/AlexSchlessingerman.shtml|archive-date=1 January 2018|access-date=31 December 2017|publisher=The Physics Factbook: An Encyclopedia of Scientific Essays}}</ref> Like many other conditions, body weight and body type are influenced by both genetic susceptibility and environment and varies greatly among individuals.<ref>{{cite book|vauthors=Kushner R|url={{GBurl|id=vWjK5etS7PMC|p=121}}|title=Treatment of the Obese Patient (Contemporary Endocrinology)|publisher=Humana Press|year=2007|isbn=978-1-59745-400-1|location=Totowa, NJ|page=158|access-date=5 April 2009}}</ref><ref name="Anes2000">{{cite journal | vauthors = Adams JP, Murphy PG | title = Obesity in anaesthesia and intensive care | journal = British Journal of Anaesthesia | volume = 85 | issue = 1 | pages = 91–108 | date = July 2000 | pmid = 10927998 | doi = 10.1093/bja/85.1.91 | doi-access = free }}</ref>

Humans have a far faster and more accurate [[throw]] than other animals.<ref>{{cite journal| vauthors = Lombardo MP, Deaner RO |date=March 2018|title=Born to Throw: The Ecological Causes that Shaped the Evolution of Throwing In Humans |journal=The Quarterly Review of Biology|language=en|volume=93|issue=1|pages=1–16|doi=10.1086/696721|s2cid=90757192|issn=0033-5770}}</ref> Humans are also among the best long-distance runners in the animal kingdom, but slower over short distances.<ref>{{cite news |url=https://www.nytimes.com/2009/10/27/health/27well.html |work=The New York Times |title=The Human Body Is Built for Distance | vauthors = Parker-Pope T |author-link1=Tara Parker-Pope |date=27 October 2009 |url-status=live |archive-url=https://web.archive.org/web/20151105211812/https://www.nytimes.com/2009/10/27/health/27well.html |archive-date=5 November 2015 }}</ref><ref name="O'Neil">{{cite web | vauthors = O'Neil D |title=Humans |url=https://anthro.palomar.edu/primate/prim_8.htm |work=Primates |publisher=Palomar College |access-date=6 January 2013 |url-status=live |archive-url=https://web.archive.org/web/20130111004211/https://anthro.palomar.edu/primate/prim_8.htm |archive-date=11 January 2013 }}</ref> Humans' thinner body hair and more productive sweat glands help avoid [[heat exhaustion]] while running for long distances.<ref>{{cite web | vauthors = John B |title=What is the role of sweating glands in balancing body temperature when running a marathon? |url=https://www.livestrong.com/article/514545-what-is-the-role-of-sweat-glands-in-balancing-body-temperature-when-running-a-marathon/ |publisher=Livestrong.com |access-date=6 January 2013 |url-status=live |archive-url=https://web.archive.org/web/20130131184339/https://www.livestrong.com/article/514545-what-is-the-role-of-sweat-glands-in-balancing-body-temperature-when-running-a-marathon/ |archive-date=31 January 2013 }}</ref> Compared to other apes, the human [[heart]] produces greater [[stroke volume]] and [[cardiac output]] and the [[aorta]] is proportionately larger.<ref>{{cite journal|last1=Shave|first1=R. E.|last2=Lieberman|first2=D. E.|last3=Drane|first3=A. L.|display-authors=etal|year=2019|title=Selection of endurance capabilities and the trade-off between pressure and volume in the evolution of the human heart|journal=PNAS|volume=116|issue=40|pages=19905–19910|doi=10.1073/pnas.1906902116|doi-access=free |pmid=31527253 |pmc=6778238|bibcode=2019PNAS..11619905S }}</ref><ref>{{cite journal|last1=Ríos|first1=L|last2=Sleeper|first2=M. M.|last3=Danforth|first3=M. D.|display-authors=etal|year=2023|title=The aorta in humans and African great apes, and cardiac output and metabolic levels in human evolution|journal=Scientific Reports|volume=13|issue=6841|page=6841|doi=10.1038/s41598-023-33675-1|pmid=37100851|pmc=10133235|bibcode=2023NatSR..13.6841R|hdl=10261/309357|hdl-access=free}}</ref>

=== Genetics ===
{{Main|Human genetics}}[[File:Human karyotype with bands and sub-bands.png|thumb|A graphical representation of the standard human [[karyotype]], including both the female (XX) and male (XY) sex chromosomes (bottom right), as well as the [[human mitochondrial genetics|mitochondrial genome]] (shown to scale as "MT" at bottom left). {{further|Karyotype}}]]

Like most animals, humans are a [[ploidy|diploid]] and [[eukaryote|eukaryotic]] species. Each [[somatic cell]] has two sets of 23 [[chromosome]]s, each set received from one parent; [[gamete]]s have only one set of chromosomes, which is a mixture of the two parental sets. Among the 23 pairs of chromosomes, there are 22 pairs of [[autosome]]s and one pair of [[sex-determination system|sex chromosomes]]. Like other mammals, humans have an [[XY sex-determination system]], so that females have the sex chromosomes XX and males have XY.<ref name="Therman1980">{{cite book | vauthors = Therman E |title=Human Chromosomes: Structure, Behavior, Effects |date=1980 |publisher=[[Springer Science+Business Media|Springer US]] |pages=112–124 |isbn=978-1-4684-0109-7 |doi=10.1007/978-1-4684-0107-3|s2cid=36686283 }}</ref> [[Gene]]s and [[Environment (biophysical)|environment]] influence human biological variation in visible characteristics, physiology, disease susceptibility and mental abilities. The exact influence of [[Environment (biophysical)|genes and environment]] on certain traits is not well understood.<ref>{{cite journal | vauthors = Edwards JH, Dent T, Kahn J | title = Monozygotic twins of different sex | journal = Journal of Medical Genetics | volume = 3 | issue = 2 | pages = 117–123 | date = June 1966 | pmid = 6007033 | pmc = 1012913 | doi = 10.1136/jmg.3.2.117 }}</ref><ref>{{cite journal | vauthors = Machin GA | title = Some causes of genotypic and phenotypic discordance in monozygotic twin pairs | journal = American Journal of Medical Genetics | volume = 61 | issue = 3 | pages = 216–228 | date = January 1996 | pmid = 8741866 | doi = 10.1002/(SICI)1096-8628(19960122)61:3<216::AID-AJMG5>3.0.CO;2-S }}</ref>

While no humans{{snd}}not even [[monozygotic twins]]{{snd}}are genetically identical,<ref>{{cite journal | vauthors = Jonsson H, Magnusdottir E, Eggertsson HP, Stefansson OA, Arnadottir GA, Eiriksson O, Zink F, Helgason EA, Jonsdottir I, Gylfason A, Jonasdottir A, Jonasdottir A, Beyter D, Steingrimsdottir T, Norddahl GL, Magnusson OT, Masson G, Halldorsson BV, Thorsteinsdottir U, Helgason A, Sulem P, Gudbjartsson DF, Stefansson K | display-authors = 6 | title = Differences between germline genomes of monozygotic twins | journal = Nature Genetics | volume = 53 | issue = 1 | pages = 27–34 | date = January 2021 | pmid = 33414551 | doi = 10.1038/s41588-020-00755-1 | s2cid = 230986741 }}</ref> two humans on average will have a genetic similarity of 99.5%-99.9%.<ref>{{cite web|title=Genetic – Understanding Human Genetic Variation|url=https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|url-status=dead|archive-url=https://web.archive.org/web/20130825143543/https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|archive-date=25 August 2013|access-date=13 December 2013|work=Human Genetic Variation|publisher=National Institute of Health (NIH)|quote=Between any two humans, the amount of genetic variation{{snd}}biochemical individuality{{snd}}is about 0.1%.}}</ref><ref>{{cite journal | vauthors = Levy S, Sutton G, Ng PC, Feuk L, Halpern AL, Walenz BP, Axelrod N, Huang J, Kirkness EF, Denisov G, Lin Y, MacDonald JR, Pang AW, Shago M, Stockwell TB, Tsiamouri A, Bafna V, Bansal V, Kravitz SA, Busam DA, Beeson KY, McIntosh TC, Remington KA, Abril JF, Gill J, Borman J, Rogers YH, Frazier ME, Scherer SW, Strausberg RL, Venter JC | display-authors = 6 | title = The diploid genome sequence of an individual human | journal = PLOS Biology | volume = 5 | issue = 10 | pages = e254 | date = September 2007 | pmid = 17803354 | pmc = 1964779 | doi = 10.1371/journal.pbio.0050254 | doi-access = free }}</ref> This makes them more [[Human genetic variation|homogeneous]] than other great apes, including chimpanzees.<ref name="REGWG2005">{{cite journal | vauthors = ((Race, Ethnicity, and Genetics Working Group)) | title = The use of racial, ethnic, and ancestral categories in human genetics research | journal = American Journal of Human Genetics | volume = 77 | issue = 4 | pages = 519–532 | date = October 2005 | pmid = 16175499 | pmc = 1275602 | doi = 10.1086/491747 }}</ref><ref name="oxf">{{cite web|title=Chimps show much greater genetic diversity than humans|url=https://www.ox.ac.uk/media/news_stories/2012/120302.html|url-status=dead|archive-url=https://web.archive.org/web/20131218091207/https://www.ox.ac.uk/media/news_stories/2012/120302.html|archive-date=18 December 2013|access-date=13 December 2013|work=Media|publisher=University of Oxford}}</ref> This small variation in human DNA compared to many other species suggests a [[population bottleneck]] during the [[Late Pleistocene]] (around 100,000 years ago), in which the human population was reduced to a small number of breeding pairs.<ref name="Harpending1998">{{cite journal | vauthors = Harpending HC, Batzer MA, Gurven M, Jorde LB, Rogers AR, Sherry ST | title = Genetic traces of ancient demography | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 4 | pages = 1961–1967 | date = February 1998 | pmid = 9465125 | pmc = 19224 | doi = 10.1073/pnas.95.4.1961 | bibcode = 1998PNAS...95.1961H | doi-access = free }}</ref><ref name="Jorde1997">{{cite journal | vauthors = Jorde LB, Rogers AR, Bamshad M, Watkins WS, Krakowiak P, Sung S, Kere J, Harpending HC | display-authors = 6 | title = Microsatellite diversity and the demographic history of modern humans | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 94 | issue = 7 | pages = 3100–3103 | date = April 1997 | pmid = 9096352 | pmc = 20328 | doi = 10.1073/pnas.94.7.3100 | bibcode = 1997PNAS...94.3100J | doi-access = free }}</ref> The forces of [[natural selection]] have continued to operate on human populations, with evidence that certain regions of the [[genome]] display [[directional selection]] in the past 15,000 years.<ref name="urlNYT">{{cite news| vauthors = Wade N |date=7 March 2007|title=Still Evolving, Human Genes Tell New Story|newspaper=The New York Times|url=https://www.nytimes.com/2006/03/07/science/07evolve.html|url-status=live|access-date=13 February 2012|archive-url=https://web.archive.org/web/20120114232231/https://www.nytimes.com/2006/03/07/science/07evolve.html|archive-date=14 January 2012}}</ref>

The [[human genome]] was first sequenced in 2001<ref>{{cite journal | vauthors = Pennisi E | author-link=Elizabeth Pennisi | title = The human genome | journal = Science | volume = 291 | issue = 5507 | pages = 1177–1180 | date = February 2001 | pmid = 11233420 | doi = 10.1126/science.291.5507.1177 | s2cid = 38355565 }}</ref> and by 2020 hundreds of thousands of genomes had been sequenced.<ref>{{cite journal | vauthors = Rotimi CN, Adeyemo AA | title = From one human genome to a complex tapestry of ancestry | journal = Nature | volume = 590 | issue = 7845 | pages = 220–221 | date = February 2021 | pmid = 33568827 | doi = 10.1038/d41586-021-00237-2 | bibcode = 2021Natur.590..220R | s2cid = 231882262 }}</ref> In 2012 the [[International HapMap Project]] had compared the genomes of 1,184 individuals from 11 populations and identified 1.6 million [[single nucleotide polymorphisms]].<ref>{{cite journal | vauthors = Altshuler DM, Gibbs RA, Peltonen L, Altshuler DM, Gibbs RA, Peltonen L, Dermitzakis E, Schaffner SF, Yu F, Peltonen L, Dermitzakis E, Bonnen PE, Altshuler DM, Gibbs RA, de Bakker PI, Deloukas P, Gabriel SB, Gwilliam R, Hunt S, Inouye M, Jia X, Palotie A, Parkin M, Whittaker P, Yu F, Chang K, Hawes A, Lewis LR, Ren Y, Wheeler D, Gibbs RA, Muzny DM, Barnes C, Darvishi K, Hurles M, Korn JM, Kristiansson K, Lee C, McCarrol SA, Nemesh J, Dermitzakis E, Keinan A, Montgomery SB, Pollack S, Price AL, Soranzo N, Bonnen PE, Gibbs RA, Gonzaga-Jauregui C, Keinan A, Price AL, Yu F, Anttila V, Brodeur W, Daly MJ, Leslie S, McVean G, Moutsianas L, Nguyen H, Schaffner SF, Zhang Q, Ghori MJ, McGinnis R, McLaren W, Pollack S, Price AL, Schaffner SF, Takeuchi F, Grossman SR, Shlyakhter I, Hostetter EB, Sabeti PC, Adebamowo CA, Foster MW, Gordon DR, Licinio J, Manca MC, Marshall PA, Matsuda I, Ngare D, Wang VO, Reddy D, Rotimi CN, Royal CD, Sharp RR, Zeng C, Brooks LD, McEwen JE | display-authors = 6 | title = Integrating common and rare genetic variation in diverse human populations | journal = Nature | volume = 467 | issue = 7311 | pages = 52–58 | date = September 2010 | pmid = 20811451 | doi = 10.1038/nature09298 | pmc = 3173859 | bibcode = 2010Natur.467...52T }}</ref> African populations harbor the highest number of private genetic variants. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers that are private to these regions, especially [[Oceania]] and [[the Americas]].<ref name="Bergstrom2020" /> By 2010 estimates, humans have approximately 22,000 genes.<ref name=Pertea2010>{{cite journal | vauthors = Pertea M, Salzberg SL | title = Between a chicken and a grape: estimating the number of human genes | journal = Genome Biology | volume = 11 | issue = 5 | page = 206 | year = 2010 | pmid = 20441615 | pmc = 2898077 | doi = 10.1186/gb-2010-11-5-206 | doi-access = free }}</ref> By comparing [[mtDNA|mitochondrial DNA]], which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose [[genetic marker]] is found in all modern humans, the so-called [[mitochondrial Eve]], must have lived around 90,000 to 200,000 years ago.<ref name="pmid3025745">{{cite journal | vauthors = Cann RL, Stoneking M, Wilson AC | title = Mitochondrial DNA and human evolution | journal = Nature | volume = 325 | issue = 6099 | pages = 31–36 | year = 1987 | pmid = 3025745 | doi = 10.1038/325031a0 | bibcode = 1987Natur.325...31C | s2cid = 4285418 }}</ref><ref>{{cite journal | vauthors = Soares P, Ermini L, Thomson N, Mormina M, Rito T, Röhl A, Salas A, Oppenheimer S, Macaulay V, Richards MB | display-authors = 6 | title = Correcting for purifying selection: an improved human mitochondrial molecular clock | journal = American Journal of Human Genetics | volume = 84 | issue = 6 | pages = 740–759 | date = June 2009 | pmid = 19500773 | pmc = 2694979 | doi = 10.1016/j.ajhg.2009.05.001}}</ref><ref>{{Cite web|url=https://www.leeds.ac.uk/news/article/245/new_molecular_clock_aids_dating_of_human_migration_history|title=University of Leeds &#124; News > Technology > New 'molecular clock' aids dating of human migration history|date=20 August 2017|archive-url=https://web.archive.org/web/20170820230218/https://www.leeds.ac.uk/news/article/245/new_molecular_clock_aids_dating_of_human_migration_history|archive-date=20 August 2017}}</ref><ref name="poz">{{cite journal | vauthors = Poznik GD, Henn BM, Yee MC, Sliwerska E, Euskirchen GM, Lin AA, Snyder M, Quintana-Murci L, Kidd JM, Underhill PA, Bustamante CD | display-authors = 6 | title = Sequencing Y chromosomes resolves discrepancy in time to common ancestor of males versus females | journal = Science | volume = 341 | issue = 6145 | pages = 562–565 | date = August 2013 | pmid = 23908239 | pmc = 4032117 | doi = 10.1126/science.1237619 | bibcode = 2013Sci...341..562P }}</ref>

=== Life cycle ===

{{See also|Childbirth|Life expectancy|}}
[[File:Tubal Pregnancy with embryo.jpg|thumb|A 10&nbsp;mm [[human embryo]] at 5 weeks]]
Most [[human reproduction]] takes place by [[internal fertilization]] via [[human sexual intercourse|sexual intercourse]], but can also occur through [[assisted reproductive technology]] procedures.<ref name="She2016">{{cite book| vauthors = Shehan CL |url={{GBurl|id=-gSeCAAAQBAJ|p=406}}|title=The Wiley Blackwell Encyclopedia of Family Studies, 4 Volume Set|date=2016|publisher=John Wiley & Sons|isbn=978-0-470-65845-1|page=406|name-list-style=vanc}}</ref> The average [[gestation]] period is 38 weeks, but a normal pregnancy can vary by up to 37 days.<ref>{{cite journal | vauthors = Jukic AM, Baird DD, [[Clarice Weinberg|Weinberg CR]], McConnaughey DR, Wilcox AJ | title = Length of human pregnancy and contributors to its natural variation | journal = Human Reproduction | volume = 28 | issue = 10 | pages = 2848–2855 | date = October 2013 | pmid = 23922246 | pmc = 3777570 | doi = 10.1093/humrep/det297 }}</ref> Embryonic development in the human covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a [[fetus]].<ref name="nursing">{{cite book | vauthors = Klossner NJ | url = {{GBurl|id=B47OVg25g-QC|q=fetal stage begins|p=103}} | title = Introductory Maternity Nursing | date = 2005 | page = 103 | publisher=Lippincott Williams & Wilkins | quote = The fetal stage is from the beginning of the 9th week after fertilization and continues until birth | isbn = 978-0-7817-6237-3 | access-date = 30 July 2022 }}</ref> Humans are able to [[Labor induction|induce early labor]] or perform a [[caesarean section]] if the child needs to be born earlier for medical reasons.<ref name="WHO2014">{{cite web|author=World Health Organization|date=November 2014|title=Preterm birth Fact sheet N°363|url=https://www.who.int/mediacentre/factsheets/fs363/en/|url-status=live|archive-url=https://web.archive.org/web/20150307050438/https://www.who.int/mediacentre/factsheets/fs363/en/|archive-date=7 March 2015|access-date=6 March 2015|work=who.int}}</ref> In developed countries, [[infant]]s are typically {{Convert|3|-|4|kg|lb|abbr=on|lk=off|0}} in weight and {{Convert|47|-|53|cm|in|abbr=on|lk=off|0}} in height at birth.<ref>{{cite journal | vauthors = Kiserud T, Benachi A, Hecher K, Perez RG, Carvalho J, Piaggio G, Platt LD | title = The World Health Organization fetal growth charts: concept, findings, interpretation, and application | journal = American Journal of Obstetrics and Gynecology | volume = 218 | issue = 2S | pages = S619–S629 | date = February 2018 | pmid = 29422204 | doi = 10.1016/j.ajog.2017.12.010 | s2cid = 46810955 | doi-access = free }}</ref><ref>{{cite web|date=18 March 2019|title=What is the average baby length? Growth chart by month|url=https://www.medicalnewstoday.com/articles/324728|access-date=18 April 2021|website=www.medicalnewstoday.com|language=en|archive-date=27 January 2021|archive-url=https://web.archive.org/web/20210127193402/https://www.medicalnewstoday.com/articles/324728|url-status=live}}</ref> However, [[low birth weight]] is common in developing countries, and contributes to the high levels of [[infant mortality]] in these regions.<ref name="Khor2003">{{cite journal | vauthors = Khor GL | title = Update on the prevalence of malnutrition among children in Asia | journal = Nepal Medical College Journal | volume = 5 | issue = 2 | pages = 113–122 | date = December 2003 | pmid = 15024783 }}</ref>

Compared with other species, human childbirth is dangerous, with a much higher risk of complications and death.<ref>{{cite journal| vauthors = Rosenberg KR |date=1992|title=The evolution of modern human childbirth |journal=American Journal of Physical Anthropology|language=en|volume=35|issue=S15|pages=89–124|doi=10.1002/ajpa.1330350605|issn=1096-8644}}</ref> The size of the fetus's head is more closely matched to the [[pelvis]] than in other primates.<ref name="Pavlicev">{{cite journal | vauthors = Pavličev M, Romero R, Mitteroecker P | title = Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma | journal = American Journal of Obstetrics and Gynecology | volume = 222 | issue = 1 | pages = 3–16 | date = January 2020 | pmid = 31251927 | doi = 10.1016/j.ajog.2019.06.043 | pmc = 9069416 | s2cid = 195761874 }}</ref> The reason for this is not completely understood,{{#tag:ref|Traditionally this has been explained by conflicting [[evolutionary pressure]]s involved in bipedalism and encephalization (called the [[obstetrical dilemma]]), but recent research suggest it might be more complicated than that.<ref name="Pavlicev" /><ref>{{cite news|title=The real reasons why childbirth is so painful and dangerous| vauthors = Barras C |date=22 December 2016|publisher=BBC}}</ref>|group=n}} but it contributes to a painful labor that can last 24 hours or more.<ref>{{cite web | vauthors = Kantrowitz B | date = 2 July 2007 | title = What Kills One Woman Every Minute of Every Day? | work = [[Newsweek]] | url = https://www.msnbc.msn.com/id/19389326/site/newsweek/ | archive-url = https://web.archive.org/web/20070628160443/https://www.msnbc.msn.com/id/19389326/site/newsweek/ | archive-date = 28 June 2007 | quote = A woman dies in childbirth every minute, most often due to uncontrolled bleeding and infection, with the world's poorest women most vulnerable. The lifetime risk is 1 in 16 in [[sub-Saharan Africa]], compared to 1 in 2,800 in [[developed countries]]. }}</ref> The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and [[natural childbirth]] remain hazardous ordeals in developing regions of the world, with [[maternal death rates]] approximately 100 times greater than in developed countries.<ref name="Rush2000">{{cite journal | vauthors = Rush D | title = Nutrition and maternal mortality in the developing world | journal = The American Journal of Clinical Nutrition | volume = 72 | issue = 1 Suppl | pages = 212S–240S | date = July 2000 | pmid = 10871588 | doi = 10.1093/ajcn/72.1.212S | doi-access = free }}</ref>

Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care is mostly done by the mother.<ref>{{cite book|vauthors=Laland KN, Brown G|url={{GBurl|id=2KcbFVBSxWYC}}|title=Sense and Nonsense: Evolutionary Perspectives on Human Behaviour|date=2011|publisher=Oxford University Press|isbn=978-0-19-958696-7|page=7|language=en|access-date=30 July 2022}}</ref> [[Altricial|Helpless at birth]], humans continue to grow for some years, typically reaching [[sexual maturity]] at 15 to 17 years of age.<ref name="Kail">{{cite book|vauthors=Kail RV, Cavanaugh JC|url={{GBurl|id=E-n5E7oyCgoC|p=296}}|title=Human Development: A Lifespan View|publisher=[[Cengage Learning]]|year=2010|isbn=978-0-495-60037-4|edition=5th|page=296|access-date=30 July 2022}}</ref><ref name="Schuiling">{{cite book|vauthors=Schuiling KD, Likis FE|url={{GBurl|id=QTDFDAAAQBAJ|p=22}}|title=Women's Gynecologic Health|publisher=[[Jones & Bartlett Learning]]|year=2016|isbn=978-1-284-12501-6|page=22|quote=The changes that occur during puberty usually happen in an ordered sequence, beginning with thelarche (breast development) at around age 10 or 11, followed by adrenarche (growth of pubic hair due to androgen stimulation), peak height velocity, and finally menarche (the onset of menses), which usually occurs around age 12 or 13.|access-date=30 July 2022}}</ref><ref name="Phillips">{{cite book|vauthors=Phillips DC|url={{GBurl|id=84StBAAAQBAJ|p=18}}|title=Encyclopedia of Educational Theory and Philosophy|publisher=[[SAGE Publications]]|year=2014|isbn=978-1-4833-6475-9|pages=18–19|quote=On average, the onset of puberty is about 18 months earlier for girls (usually starting around the age of 10 or 11 and lasting until they are 15 to 17) than for boys (who usually begin puberty at about the age of 11 to 12 and complete it by the age of 16 to 17, on average).|access-date=30 July 2022}}</ref> The human life span has been split into various stages ranging from three to twelve. Common stages include [[Infant|infancy]], [[childhood]], [[adolescence]], [[adult]]hood and [[old age]].<ref>{{cite journal| vauthors = Mintz S |date=1993|title=Life stages|journal=Encyclopedia of American Social History|volume=3|pages=7–33}}</ref> The lengths of these stages have varied across cultures and time periods but is typified by an unusually rapid growth spurt during adolescence.<ref>{{cite journal | vauthors = Soliman A, De Sanctis V, Elalaily R, Bedair S | title = Advances in pubertal growth and factors influencing it: Can we increase pubertal growth? | journal = Indian Journal of Endocrinology and Metabolism | volume = 18 | issue = Suppl 1 | pages = S53-62 | date = November 2014 | pmid = 25538878 | pmc = 4266869 | doi = 10.4103/2230-8210.145075 | doi-access = free }}</ref> Human females undergo [[menopause]] and become [[Infertility|infertile]] at around the age of 50.<ref>{{cite journal | vauthors = Walker ML, Herndon JG | title = Menopause in nonhuman primates? | journal = Biology of Reproduction | volume = 79 | issue = 3 | pages = 398–406 | date = September 2008 | pmid = 18495681 | pmc = 2553520 | doi = 10.1095/biolreprod.108.068536 }}</ref> It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring, and in turn their children (the [[grandmother hypothesis]]), rather than by continuing to bear children into old age.<ref name="Diamond1997">{{cite book | vauthors = Diamond J |author-link=Jared Diamond |title=Why is Sex Fun? The Evolution of Human Sexuality |publisher=Basic Books |location=New York|year=1997 |pages=167–170 |isbn=978-0-465-03127-6}}</ref><ref name="Peccei2001">{{cite journal | vauthors = Peccei JS |title= Menopause: Adaptation or epiphenomenon? |journal=Evolutionary Anthropology |volume=10 |issue=2 |year=2001 |pages=43–57 |doi=10.1002/evan.1013|s2cid=1665503 }}</ref>

The life span of an individual depends on two major factors, genetics and lifestyle choices.<ref name="USC">{{cite news | vauthors = Marziali C |date=7 December 2010 |title=Reaching Toward the Fountain of Youth |url=https://uscnews.usc.edu/health/reaching_toward_the_fountain_of_youth.html|archive-url=https://web.archive.org/web/20101213203112/https://uscnews.usc.edu/health/reaching_toward_the_fountain_of_youth.html|url-status=dead|archive-date=13 December 2010 |work=USC Trojan Family Magazine |access-date=7 December 2010}}</ref> For various reasons, including biological/genetic causes, women live on average about four years longer than men.<ref>{{cite web | vauthors = Kalben BB |title=Why Men Die Younger: Causes of Mortality Differences by Sex |publisher=Society of Actuaries |year=2002 |url=https://www.soa.org/news-and-publications/publications/other-publications/monographs/m-li01-1-toc.aspx |url-status=live |archive-url=https://web.archive.org/web/20130701185241/https://www.soa.org/news-and-publications/publications/other-publications/monographs/m-li01-1-toc.aspx |archive-date=1 July 2013 }}</ref> {{as of|2018|}}, the global average [[life expectancy at birth]] of a girl is estimated to be 74.9 years compared to 70.4 for a boy.<ref>{{cite web|date=2018|title=Life expectancy at birth, female (years)|url=https://data.worldbank.org/indicator/SP.DYN.LE00.FE.IN|access-date=13 October 2020|website=World Bank|archive-date=24 January 2021|archive-url=https://web.archive.org/web/20210124203646/https://data.worldbank.org/indicator/SP.DYN.LE00.FE.IN|url-status=live}}</ref><ref>{{cite web|date=2018|title=Life expectancy at birth, male (years)|url=https://data.worldbank.org/indicator/SP.DYN.LE00.MA.IN|access-date=13 October 2020|website=World Bank|archive-date=24 February 2021|archive-url=https://web.archive.org/web/20210224133034/https://data.worldbank.org/indicator/SP.DYN.LE00.MA.IN|url-status=live}}</ref> There are significant geographical variations in human life expectancy, mostly correlated with economic development{{snd}}for example, life expectancy at birth in [[Hong Kong]] is 87.6&nbsp;years for girls and 81.8 for boys, while in the [[Central African Republic]], it is 55.0&nbsp;years for girls and 50.6 for boys.<ref>{{cite book | vauthors = Conceição P, etal | title = Human Development Report | date = 2019 | publisher = United Nations Development Programme | url = https://hdr.undp.org/sites/default/files/hdr2019.pdf | isbn = 978-92-1-126439-5 | access-date = 30 July 2022 | archive-date = 20 March 2021 | archive-url = https://web.archive.org/web/20210320094952/http://hdr.undp.org/sites/default/files/hdr2019.pdf | url-status = live }}</ref><ref name="MLT">{{cite web|url=https://hdr.undp.org/sites/all/themes/hdr_theme/country-notes/MLT.pdf|title=Human Development Report 2019|language=en|publisher=[[United Nations Development Programme]]|access-date=30 July 2022|archive-date=22 April 2022|archive-url=https://web.archive.org/web/20220422102059/https://hdr.undp.org/sites/all/themes/hdr_theme/country-notes/MLT.pdf|url-status=dead}}</ref> The developed world is generally aging, with the median age around 40 years. In the [[third world|developing world]], the median age is between 15 and 20 years. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older.<ref>{{cite web | url = https://www.cia.gov/library/publications/the-world-factbook/ | title = The World Factbook | archive-url = https://web.archive.org/web/20090912045414/https://www.cia.gov/library/publications/the-world-factbook/ | archive-date = 12 September 2009 | publisher = U.S. Central Intelligence Agency | access-date = 2 April 2005 }}</ref> In 2012, the United Nations estimated that there were 316,600 living [[centenarians]] (humans of age 100 or older) worldwide.<ref name="WORLD2012">{{cite web|url=http://www.unfpa.org/webdav/site/global/shared/documents/publications/2012/UNFPA-Report-Chapter1.pdf|title=Chapter 1: Setting the Scene|year=2012|publisher=UNFPA|access-date=11 January 2013|archive-url=https://web.archive.org/web/20130612052543/http://www.unfpa.org/webdav/site/global/shared/documents/publications/2012/UNFPA-Report-Chapter1.pdf|archive-date=12 June 2013}}</ref>
{| class="wikitable" style="width: 80%; margin-left: auto; margin-right: auto; border: none;"
|+
! colspan="5" | Human life stages
|-
|[[File:Redheaded child mesmerized 2.jpg|100px|center]]
|[[File:Ромський хлопчик (Мукачево).jpg|100px|center]]
|[[File:Boy in Dar es Salaam (14453809622).jpg|100px|center]]
|[[File:Pataxo001.jpg|100px|center]]
|[[File:An old age.JPG|100px|center]]
|-
|[[File:Baby playing with yellow paint. Work by Dutch artist Peter Klashorst entitled "Experimental".jpg|100px|center]]
|[[File:Ethnie dong 6511a.jpg|100px|center]]
|[[File:Portrait of a Persian lady in Iran, 10-08-2006 (cropped).jpg|100px|center]]
|[[File:Punjabi woman smile.jpg|100px|center]]
|[[File:HappyPensioneer.jpg|100px|center]]
|- style="text-align: center;"
|style="width: 20%"|[[Infant]] boy and girl
|style="width: 20%"|Boy and girl before [[puberty]] ([[child]]ren)
|style="width: 20%"|[[Adolescent]] male and female
|style="width: 20%"|[[Adult]] man and woman
|style="width: 20%"|[[Elderly]] man and woman
|}

=== Diet ===
{{Main|Human nutrition}}
[[File:Preparing The Feast.jpg|thumb|right|Humans living in [[Bali]], [[Indonesia]], preparing a meal]]Humans are [[omnivorous]], capable of consuming a wide variety of plant and animal material.<ref>{{cite journal | vauthors = Haenel H | title = Phylogenesis and nutrition | journal = Die Nahrung | volume = 33 | issue = 9 | pages = 867–887 | year = 1989 | pmid = 2697806 }}</ref><ref>{{cite book | veditors = Ungar PS |year=2007 | vauthors = Cordain L |title=Evolution of the human diet: the known, the unknown and the unknowable |chapter=Implications of Plio-pleistocene diets for modern humans |quote=Since the evolutionary split between hominins and [[pongids]] approximately 7 million years ago, the available evidence shows that all species of hominins ate an omnivorous diet composed of minimally processed, wild-plant, and animal foods. |pages=264–265}}</ref> Human groups have adopted a range of diets from purely [[vegan]] to primarily [[carnivorous]]. In some cases, dietary restrictions in humans can lead to [[deficiency diseases]]; however, stable human groups have adapted to many dietary patterns through both genetic specialization and cultural conventions to use nutritionally balanced food sources.<ref>{{cite journal | title = Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets | journal = Journal of the American Dietetic Association | volume = 103 | issue = 6 | pages = 748–765 | date = June 2003 | pmid = 12778049 | doi = 10.1053/jada.2003.50142 | author1 = American Dietetic Association }}</ref> The human diet is prominently reflected in human culture and has led to the development of [[food science]].<ref name="Crittenden-2017">{{cite journal| vauthors = Crittenden AN, Schnorr SL |date=2017|title=Current views on hunter-gatherer nutrition and the evolution of the human diet |journal=American Journal of Physical Anthropology |volume=162 |issue=S63 |pages=84–109 |doi=10.1002/ajpa.23148 |pmid=28105723|doi-access=free }}</ref>

Until the development of agriculture, ''Homo sapiens'' employed a hunter-gatherer method as their sole means of food collection.<ref name="Crittenden-2017" /> This involved combining stationary food sources (such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic mollusks) with [[Game (food)|wild game]], which must be hunted and captured in order to be consumed.<ref>{{cite journal | vauthors = Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, O'Keefe JH, Brand-Miller J | display-authors = 6 | title = Origins and evolution of the Western diet: health implications for the 21st century | journal = The American Journal of Clinical Nutrition | volume = 81 | issue = 2 | pages = 341–354 | date = February 2005 | pmid = 15699220 | doi = 10.1093/ajcn.81.2.341 | name-list-style = vanc | doi-access = free }}</ref> It has been proposed that humans have used fire to prepare and [[cooking|cook]] food since the time of ''[[Homo erectus]]''.<ref>{{cite journal | vauthors = Ulijaszek SJ | title = Human eating behaviour in an evolutionary ecological context | journal = The Proceedings of the Nutrition Society | volume = 61 | issue = 4 | pages = 517–526 | date = November 2002 | pmid = 12691181 | doi = 10.1079/PNS2002180 | doi-access = free }}</ref> Human [[domestication]] of wild plants began about 11,700 years ago, leading to the [[History of agriculture|development of agriculture]],<ref>{{cite journal|title=Unearthing the origins of agriculture|author=John Carey|doi=10.1073/pnas.2304407120|journal=[[Proceedings of the National Academy of Sciences]]|volume=120|issue=15|date=2023|pages=e2304407120 |doi-access=free|pmid=37018195 |pmc=10104519|bibcode=2023PNAS..12004407C }}</ref> a gradual process called the [[Neolithic Revolution]].<ref>{{cite journal|title=Can models of evolutionary transition clarify the debates over the Neolithic Revolution?|author1=Ayelet Shavit|author2=Gonen Sharon|journal=[[Philosophical Transactions of the Royal Society B]]|date=2023|volume=378|issue=1872|doi=10.1098/rstb.2021.0413 |pmid=36688395 |pmc=9869441 }}}</ref> These dietary changes may also have altered human biology; the spread of [[dairy farming]] provided a new and rich source of food, leading to the evolution of the ability to digest [[lactose]] in some adults.<ref>{{cite journal | vauthors = Krebs JR | title = The gourmet ape: evolution and human food preferences | journal = The American Journal of Clinical Nutrition | volume = 90 | issue = 3 | pages = 707S–711S | date = September 2009 | pmid = 19656837 | doi = 10.3945/ajcn.2009.27462B | doi-access = free }}</ref><ref>{{cite journal | vauthors = Holden C, Mace R | title = Phylogenetic analysis of the evolution of lactose digestion in adults | journal = Human Biology | volume = 69 | issue = 5 | pages = 605–628 | date = October 1997 | pmid = 9299882 }}</ref> The types of food consumed, and how they are prepared, have varied widely by time, location, and culture.<ref>{{cite web|vauthors=Gibbons A|title=The Evolution of Diet|url=https://www.nationalgeographic.com/foodfeatures/evolution-of-diet/|access-date=18 April 2021|website=National Geographic|archive-date=18 August 2014|archive-url=https://web.archive.org/web/20140818204010/https://www.nationalgeographic.com/foodfeatures/evolution-of-diet/|url-status=live}}</ref><ref>{{cite journal|vauthors=Ritchie H, Roser M|date=20 August 2017|title=Diet Compositions|url=https://ourworldindata.org/diet-compositions|journal=Our World in Data|access-date=30 July 2022|archive-date=25 August 2021|archive-url=https://web.archive.org/web/20210825210934/https://ourworldindata.org/diet-compositions|url-status=live}}</ref>

In general, humans can survive for up to eight weeks without food, depending on stored body fat.<ref>{{cite web|vauthors=Lieberson AD|date=2004|title=How Long Can a Person Survive without Food?|url=https://www.scientificamerican.com/article/how-long-can-a-person-survive-without-food/|access-date=18 April 2021|website=Scientific American|language=en|archive-date=14 February 2019|archive-url=https://web.archive.org/web/20190214012729/https://www.scientificamerican.com/article/how-long-can-a-person-survive-without-food/|url-status=live}}</ref> Survival without water is usually limited to three or four days, with a maximum of one week.<ref>{{cite web|vauthors=Spector D|date=9 March 2018|title=Here's how many days a person can survive without water|url=https://www.businessinsider.com.au/how-many-days-can-you-survive-without-water-2014-5|access-date=18 April 2021|website=Business Insider Australia|language=en|archive-date=26 June 2014|archive-url=https://web.archive.org/web/20140626030756/https://www.businessinsider.com.au/how-many-days-can-you-survive-without-water-2014-5|url-status=live}}</ref> In 2020 it is estimated 9 million humans die every year from causes directly or indirectly related to [[starvation]].<ref>{{cite web|vauthors=Holmes J|title=Losing 25,000 to Hunger Every Day|url=https://www.un.org/en/chronicle/article/losing-25000-hunger-every-day|access-date=18 April 2021|website=United Nations|language=en|archive-date=27 May 2020|archive-url=https://web.archive.org/web/20200527235650/https://www.un.org/en/chronicle/article/losing-25000-hunger-every-day|url-status=live}}</ref><ref>{{cite web|vauthors=Mai HJ|date=2020|title=U.N. Warns Number Of People Starving To Death Could Double Amid Pandemic|url=https://www.npr.org/sections/coronavirus-live-updates/2020/05/05/850470436/u-n-warns-number-of-people-starving-to-death-could-double-amid-pandemic|access-date=18 April 2021|website=NPR |language=en|archive-date=28 June 2021|archive-url=https://web.archive.org/web/20210628090826/https://www.npr.org/sections/coronavirus-live-updates/2020/05/05/850470436/u-n-warns-number-of-people-starving-to-death-could-double-amid-pandemic|url-status=live}}</ref> Childhood malnutrition is also common and contributes to the [[Disease burden|global burden of disease]].<ref>{{cite journal | vauthors = Murray CJ, Lopez AD | title = Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study | journal = Lancet | volume = 349 | issue = 9063 | pages = 1436–1442 | date = May 1997 | pmid = 9164317 | doi = 10.1016/S0140-6736(96)07495-8 | s2cid = 2569153 }}</ref> However, global food distribution is not even, and [[obesity]] among some human populations has increased rapidly, leading to health complications and increased mortality in some [[developed country|developed]] and a few [[developing countries]]. Worldwide, over one billion people are obese,<ref name=Haslam>{{cite journal | vauthors = Haslam DW, James WP | title = Obesity | journal = Lancet | volume = 366 | issue = 9492 | pages = 1197–1209 | date = October 2005 | pmid = 16198769 | doi = 10.1016/S0140-6736(05)67483-1 | s2cid = 208791491 }}</ref> while in the United States 35% of people are obese, leading to this being described as an "[[Epidemiology of obesity|obesity epidemic]]."<ref name=Catenacci>{{cite journal | vauthors = Catenacci VA, Hill JO, Wyatt HR | title = The obesity epidemic | journal = Clinics in Chest Medicine | volume = 30 | issue = 3 | pages = 415–444, vii | date = September 2009 | pmid = 19700042 | doi = 10.1016/j.ccm.2009.05.001 }}</ref> Obesity is caused by consuming more [[calorie]]s than are expended, so excessive weight gain is usually caused by an energy-dense diet.<ref name=Haslam />

=== Biological variation ===
{{Main|Human genetic variation}}

[[File:Genetic Variation.jpg|upright=1.3|thumb|Changes in the number and order of genes (A–D) create genetic diversity within and between population.]]
There is biological variation in the human species{{snd}}with traits such as [[blood type]], [[genetic diseases]], [[Human skull|cranial features]], [[Human face|facial features]], [[organ systems]], [[eye color]], [[hair color]] and [[hair texture|texture]], [[Human height|height]] and [[Body shape|build]], and [[Human skin color|skin color]] varying across the globe. The typical height of an adult human is between {{Convert|1.4|and|1.9|m|ftin|abbr=on}}, although this varies significantly depending on sex, [[ethnic origin]], and family bloodlines.<ref>{{cite journal | vauthors = de Beer H | title = Observations on the history of Dutch physical stature from the late-Middle Ages to the present | journal = Economics and Human Biology | volume = 2 | issue = 1 | pages = 45–55 | date = March 2004 | pmid = 15463992 | doi = 10.1016/j.ehb.2003.11.001 }}</ref><ref name="adapt2">{{cite web | vauthors = O'Neil D |title=Adapting to Climate Extremes |url=https://anthro.palomar.edu/adapt/adapt_2.htm |work=Human Biological Adaptability |publisher=Palomar College |access-date=6 January 2013 |url-status=live |archive-url= https://web.archive.org/web/20130106211840/https://anthro.palomar.edu/adapt/adapt_2.htm |archive-date=6 January 2013 }}</ref> Body size is partly determined by genes and is also significantly influenced by environmental factors such as [[diet (nutrition)|diet]], exercise, and [[sleep pattern]]s.<ref>{{cite journal | vauthors = Rask-Andersen M, Karlsson T, Ek WE, Johansson Å | title = Gene-environment interaction study for BMI reveals interactions between genetic factors and physical activity, alcohol consumption and socioeconomic status | journal = PLOS Genetics | volume = 13 | issue = 9 | pages = e1006977 | date = September 2017 | pmid = 28873402 | pmc = 5600404 | doi = 10.1371/journal.pgen.1006977 | doi-access = free }}</ref>

There is evidence that populations have adapted genetically to various external factors. The genes that allow adult humans to [[Lactose tolerance|digest lactose]] are present in high frequencies in populations that have long histories of cattle domestication and are more dependent on [[cow milk]].<ref>{{cite journal | vauthors = Beja-Pereira A, Luikart G, England PR, Bradley DG, Jann OC, Bertorelle G, Chamberlain AT, Nunes TP, Metodiev S, Ferrand N, Erhardt G | display-authors = 6 | title = Gene-culture coevolution between cattle milk protein genes and human lactase genes | journal = Nature Genetics | volume = 35 | issue = 4 | pages = 311–313 | date = December 2003 | pmid = 14634648 | doi = 10.1038/ng1263 | s2cid = 20415396 }}</ref> [[Sickle cell anemia]], which may provide increased resistance to [[malaria]], is frequent in populations where [[malaria]] is endemic.<ref name="Hedrick 2011">{{cite journal | vauthors = Hedrick PW | title = Population genetics of malaria resistance in humans | journal = Heredity | volume = 107 | issue = 4 | pages = 283–304 | date = October 2011 | pmid = 21427751 | pmc = 3182497 | doi = 10.1038/hdy.2011.16 }}</ref><ref name="Weatherall 2008">{{cite journal | vauthors = Weatherall DJ | title = Genetic variation and susceptibility to infection: the red cell and malaria | journal = British Journal of Haematology | volume = 141 | issue = 3 | pages = 276–286 | date = May 2008 | pmid = 18410566 | doi = 10.1111/j.1365-2141.2008.07085.x | s2cid = 28191911 | doi-access = free }}</ref> Populations that have for a very long time inhabited specific climates tend to have developed specific [[phenotype]]s that are beneficial for those environments{{snd}}[[Allen's rule|short stature and stocky build in cold regions]], tall and lanky in hot regions, and with high lung capacities or other [[High-altitude adaptation in humans|adaptations at high altitudes]].<ref>{{cite journal| vauthors = Shelomi M, Zeuss D |date=5 April 2017|title=Bergmann's and Allen's Rules in Native European and Mediterranean Phasmatodea |journal=Frontiers in Ecology and Evolution|volume=5|doi=10.3389/fevo.2017.00025|s2cid=34882477|issn=2296-701X|doi-access=free|hdl=11858/00-001M-0000-002C-DD87-4|hdl-access=free}}</ref> Some populations have evolved highly unique adaptations to very specific environmental conditions, such as those advantageous to ocean-dwelling lifestyles and [[freediving]] in the [[Bajau]].<ref name="Ilardo2018">{{cite journal | vauthors = Ilardo MA, Moltke I, Korneliussen TS, Cheng J, Stern AJ, Racimo F, de Barros Damgaard P, Sikora M, Seguin-Orlando A, Rasmussen S, van den Munckhof IC, Ter Horst R, Joosten LA, Netea MG, Salingkat S, Nielsen R, Willerslev E | display-authors = 6 | title = Physiological and Genetic Adaptations to Diving in Sea Nomads | journal = Cell | volume = 173 | issue = 3 | pages = 569–580.e15 | date = April 2018 | pmid = 29677510 | doi = 10.1016/j.cell.2018.03.054 | doi-access = free }}</ref>

Human hair ranges in color from [[Red hair|red]] to [[blond]] to [[Brown hair|brown]] to [[Black hair|black]], which is the most frequent.<ref>{{cite journal|vauthors=Rogers AR, Iltis D, Wooding S|year=2004|title=Genetic variation at the MC1R locus and the time since loss of human body hair|journal=Current Anthropology|volume=45|issue=1|pages=105–08|doi=10.1086/381006|s2cid=224795768}}</ref> Hair color depends on the amount of [[melanin]], with concentrations fading with increased age, leading to [[Grey hair|grey]] or even white hair. Skin color can range from [[Dark skin|darkest brown]] to [[Light skin|lightest peach]], or even nearly white or colorless in cases of [[albinism]].<ref name="roberts1">{{cite book| vauthors = Roberts D |title=Fatal Invention|publisher=The New Press|year=2011|location=London & New York}}</ref> It tends to vary [[Clinal variation|clinally]] and generally correlates with the level of [[Ultraviolet|ultraviolet radiation]] in a particular geographic area, with darker skin mostly around the equator.<ref name="jabl04">{{cite journal|vauthors=Nina J|year=2004|title=The evolution of human skin and skin color|journal=Annual Review of Anthropology|volume=33|pages=585–623|doi=10.1146/annurev.anthro.33.070203.143955}}</ref> Skin darkening may have evolved as protection against ultraviolet solar radiation.<ref>{{cite journal | vauthors = Jablonski NG, Chaplin G | title = Colloquium paper: human skin pigmentation as an adaptation to UV radiation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = Supplement_2 | pages = 8962–8968 | date = May 2010 | pmid = 20445093 | pmc = 3024016 | doi = 10.1073/pnas.0914628107 | bibcode = 2010PNAS..107.8962J | doi-access = free }}</ref> Light skin pigmentation protects against depletion of [[vitamin D]], which requires [[sunlight]] to make.<ref>{{cite journal | vauthors = Jablonski NG, Chaplin G | title = The evolution of human skin coloration | journal = Journal of Human Evolution | volume = 39 | issue = 1 | pages = 57–106 | date = July 2000 | pmid = 10896812 | doi = 10.1006/jhev.2000.0403 | url = https://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf | archive-url = https://web.archive.org/web/20120114203210/https://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf | archive-date = 14 January 2012 }}</ref> Human skin also has a capacity to darken (tan) in response to exposure to ultraviolet radiation.<ref>{{cite journal | vauthors = Harding RM, Healy E, Ray AJ, Ellis NS, Flanagan N, Todd C, Dixon C, Sajantila A, Jackson IJ, Birch-Machin MA, Rees JL | display-authors = 6 | title = Evidence for variable selective pressures at MC1R | journal = American Journal of Human Genetics | volume = 66 | issue = 4 | pages = 1351–1361 | date = April 2000 | pmid = 10733465 | pmc = 1288200 | doi = 10.1086/302863 }}</ref><ref>{{cite book | vauthors = Robin A | date = 1991 | title = Biological Perspectives on Human Pigmentation | location = Cambridge | publisher = Cambridge University Press }}</ref>[[File:Seti1a.jpg|thumb|A [[Berbers|Libyan]], a [[Nubians|Nubian]], a [[Syrian people|Syrian]], and an [[Egyptians|Egyptian]], drawing by an unknown artist after a mural of the tomb of [[Seti I]]]]

There is relatively little variation between human geographical populations, and most of the variation that occurs is at the individual level.<ref name="roberts1" /><ref name="hgp">{{cite web|title=The Science Behind the Human Genome Project|url=https://www.ornl.gov/sci/techresources/Human_Genome/project/info.shtml|url-status=dead|archive-url=https://web.archive.org/web/20130102065343/https://www.ornl.gov/sci/techresources/Human_Genome/project/info.shtml|archive-date=2 January 2013|access-date=6 January 2013|work=Human Genome Project|publisher=US Department of Energy|quote=Almost all (99.9%) nucleotide bases are exactly the same in all people.}}</ref><ref name="enr1">{{cite web| vauthors = O'Neil D | title=Ethnicity and Race: Overview|url=https://anthro.palomar.edu/ethnicity/ethnic_1.htm#return_from_ethnic_identity_question|url-status=live|archive-url=https://web.archive.org/web/20130106212622/https://anthro.palomar.edu/ethnicity/ethnic_1.htm#return_from_ethnic_identity_question|archive-date=6 January 2013|access-date=6 January 2013|publisher=Palomar College}}</ref> Much of human variation is continuous, often with no clear points of demarcation.<ref name="pmid15507998">{{cite journal | vauthors = Keita SO, Kittles RA, Royal CD, Bonney GE, Furbert-Harris P, Dunston GM, Rotimi CN | title = Conceptualizing human variation | journal = Nature Genetics | volume = 36 | issue = 11 Suppl | pages = S17-20 | date = November 2004 | pmid = 15507998 | doi = 10.1038/ng1455 | doi-access = free }}</ref><ref name="vary02">{{cite web|title=Models of Classification|url=https://anthro.palomar.edu/vary/vary_2.htm|url-status=dead|archive-url=https://web.archive.org/web/20130106212400/https://anthro.palomar.edu/vary/vary_2.htm|archive-date=6 January 2013|access-date=6 January 2013|work=Modern Human Variation|publisher=Palomar College|vauthors=O'Neil D}}</ref><ref>{{cite journal|vauthors=Jablonski N|year=2004|title=The evolution of human skin and skin color|journal=Annual Review of Anthropology|volume=33|pages=585–623|doi=10.1146/annurev.anthro.33.070203.143955}}</ref><ref name="Palmie2007">{{cite journal|vauthors=Palmié S|date=May 2007|title=Genomics, divination, 'racecraft'|journal=American Ethnologist|volume=34|issue=2|pages=205–222|doi=10.1525/ae.2007.34.2.205}}</ref> Genetic data shows that no matter how population groups are defined, two people from the same population group are almost as different from each other as two people from any two different population groups.<ref>{{cite web|title=Genetic – Understanding Human Genetic Variation|url=https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|url-status=dead|archive-url=https://web.archive.org/web/20130825143543/https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|archive-date=25 August 2013|access-date=13 December 2013|work=Human Genetic Variation|publisher=National Institute of Health (NIH)|quote=In fact, research results consistently demonstrate that about 85 percent of all human genetic variation exists within human populations, whereas about only 15 percent of variation exists between populations.}}</ref><ref name="goodman1">{{cite web| vauthors = Goodman A |title=Interview with Alan Goodman|url=https://www.pbs.org/race/000_About/002_04-background-01-07.htm|url-status=live|archive-url=https://web.archive.org/web/20121029063805/https://www.pbs.org/race/000_About/002_04-background-01-07.htm|archive-date=29 October 2012|access-date=6 January 2013|work=Race Power of and Illusion|publisher=PBS}}</ref><ref>{{cite book| vauthors = Marks J |year=2010|chapter=Ten facts about human variation |title=Human Evolutionary Biology| veditors = Muehlenbein M |location=New York|publisher=Cambridge University Press|url=https://personal.uncc.edu/jmarks/pubs/tenfacts.pdf|url-status=dead|archive-url=https://web.archive.org/web/20120415012646/https://personal.uncc.edu/jmarks/pubs/tenfacts.pdf|archive-date=15 April 2012|access-date=5 September 2013}}</ref> Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other.<ref name="jablo04">{{cite journal|vauthors=Nina J|year=2004|title=The evolution of human skin and skin color|journal=Annual Review of Anthropology|volume=33|pages=585–623|doi=10.1146/annurev.anthro.33.070203.143955|quote=genetic evidence [demonstrate] that strong levels of natural selection acted about 1.2 mya to produce darkly pigmented skin in early members of the genus Homo}}</ref><ref>{{cite web|title=Overview|url=https://anthro.palomar.edu/vary/vary_1.htm|url-status=dead|archive-url=https://web.archive.org/web/20121105101522/https://anthro.palomar.edu/vary/vary_1.htm|archive-date=5 November 2012|access-date=6 January 2013|work=Modern Human Variation|publisher=Palomar College|vauthors=O'Neil D}}</ref>

Genetic research has demonstrated that human populations native to the [[African continent]] are the most genetically diverse<ref name="Jorde2000">{{cite journal | vauthors = Jorde LB, Watkins WS, Bamshad MJ, Dixon ME, Ricker CE, Seielstad MT, Batzer MA | title = The distribution of human genetic diversity: a comparison of mitochondrial, autosomal, and Y-chromosome data | journal = American Journal of Human Genetics | volume = 66 | issue = 3 | pages = 979–988 | date = March 2000 | pmid = 10712212 | pmc = 1288178 | doi = 10.1086/302825 }}</ref> and genetic diversity decreases with migratory distance from Africa, possibly the result of [[Evolutionary bottleneck|bottlenecks]] during human migration.<ref name="sciencedaily.com">{{cite web |date=19 July 2007 |title=New Research Proves Single Origin Of Humans In Africa |url=https://www.sciencedaily.com/releases/2007/07/070718140829.htm |website=[[Science Daily]] |access-date=5 September 2011 |url-status=live |archive-url=https://web.archive.org/web/20111104103559/https://www.sciencedaily.com/releases/2007/07/070718140829.htm |archive-date=4 November 2011 }}</ref><ref>{{cite journal | vauthors = Manica A, Amos W, Balloux F, Hanihara T | title = The effect of ancient population bottlenecks on human phenotypic variation | journal = Nature | volume = 448 | issue = 7151 | pages = 346–348 | date = July 2007 | pmid = 17637668 | pmc = 1978547 | doi = 10.1038/nature05951 | author-link3 = Francois Balloux | bibcode = 2007Natur.448..346M }}</ref> These non-African populations acquired new genetic inputs from local [[Interbreeding between archaic and modern humans|admixture with archaic populations]] and have much greater variation from [[Neanderthals]] and [[Denisovans]] than is found in Africa,<ref name="Bergstrom2020">{{cite journal | vauthors = Bergström A, McCarthy SA, Hui R, Almarri MA, Ayub Q, Danecek P, Chen Y, Felkel S, Hallast P, Kamm J, Blanché H, Deleuze JF, Cann H, Mallick S, Reich D, Sandhu MS, Skoglund P, Scally A, Xue Y, Durbin R, Tyler-Smith C | display-authors = 6 | title = Insights into human genetic variation and population history from 929 diverse genomes | journal = Science | volume = 367 | issue = 6484 | pages = eaay5012 | date = March 2020 | pmid = 32193295 | pmc = 7115999 | doi = 10.1126/science.aay5012 |quote=Populations in central and southern Africa, the Americas, and Oceania each harbor tens to hundreds of thousands of ''private'', common genetic variants. Most of these variants arose as new mutations rather than through archaic introgression, except in Oceanian populations, where many private variants derive from Denisovan admixture.}}</ref> though Neanderthal admixture into African populations may be underestimated.<ref name="pmid32004458">{{cite journal | vauthors = Chen L, Wolf AB, Fu W, Li L, Akey JM | title = Identifying and Interpreting Apparent Neanderthal Ancestry in African Individuals | journal = Cell | volume = 180 | issue = 4 | pages = 677–687.e16 | date = February 2020 | pmid = 32004458 | pmc = | doi = 10.1016/j.cell.2020.01.012 | s2cid = 210955842 | doi-access = free }}</ref> Furthermore, recent studies have found that populations in [[sub-Saharan Africa]], and particularly [[West Africa]], have ancestral genetic variation which predates modern humans and has been lost in most non-African populations. Some of this ancestry is thought to originate from admixture with an [[Interbreeding between archaic and modern humans#Archaic African hominins|unknown archaic hominin]] that diverged before the split of Neanderthals and modern humans.<ref name="Bergstrom2020a">{{cite journal | vauthors = Bergström A, McCarthy SA, Hui R, Almarri MA, Ayub Q, Danecek P, Chen Y, Felkel S, Hallast P, Kamm J, Blanché H, Deleuze JF, Cann H, Mallick S, Reich D, Sandhu MS, Skoglund P, Scally A, Xue Y, Durbin R, Tyler-Smith C | display-authors = 6 | title = Insights into human genetic variation and population history from 929 diverse genomes | journal = Science | volume = 367 | issue = 6484 | pages = eaay5012 | date = March 2020 | pmid = 32193295 | pmc = 7115999 | doi = 10.1126/science.aay5012 |quote=An analysis of archaic sequences in modern populations identifies ancestral genetic variation in African populations that likely predates modern humans and has been lost in most non-African populations.}}</ref><ref name="Durvasula2020">{{cite journal | vauthors = Durvasula A, Sankararaman S | title = Recovering signals of ghost archaic introgression in African populations | journal = Science Advances | volume = 6 | issue = 7 | pages = eaax5097 | date = February 2020 | pmid = 32095519 | pmc = 7015685 | doi = 10.1126/sciadv.aax5097 | bibcode = 2020SciA....6.5097D |quote=Our analyses of site frequency spectra indicate that these populations derive 2 to 19% of their genetic ancestry from an archaic population that diverged before the split of Neanderthals and modern humans.}}</ref>

Humans are a [[Gonochorism|gonochoric]] species, meaning they are divided into male and female [[sex]]es.<ref>{{Cite book|url={{GBurl|id=z4pXRaZAkdkC|q=humans are dioecious genetics|p=75}}|title=Genetics: A Conceptual Approach|vauthors=Pierce BA|date=2012|publisher=Macmillan|isbn=978-1-4292-3252-4|pages=75|language=en|access-date=30 July 2022}}</ref><ref>{{Cite book|vauthors=Muehlenbein MP|url={{GBurl|id=1VXX1jkhPH8C|q=humans are dioecious biology|pg=PT57}}}|title=Human Evolutionary Biology|date=29 July 2010|publisher=Cambridge University Press|isbn=978-0-521-87948-4|veditors=Jones J|page=74|language=en|access-date=30 July 2022}}</ref><ref>{{Cite book|vauthors=Fusco G, Minelli A|url={{GBurl|id=AKGsDwAAQBAJ|q=homo sapiens gonochoric|p=304}}|title=The Biology of Reproduction|date=10 October 2019|publisher=Cambridge University Press|isbn=978-1-108-49985-9|page=304|language=en|access-date=30 July 2022}}</ref> The greatest degree of genetic [[Sex differences in humans|variation exists between males and females]]. While the [[nucleotide diversity|nucleotide]] genetic variation of individuals of the same sex across global populations is no greater than 0.1%–0.5%, the genetic difference between [[Man|males]] and [[woman|females]] is between 1% and 2%. Males on average are 15% heavier and {{Convert|15|cm|in|abbr=on|lk=off|0}} taller than females.<ref name="Gustafsson">{{cite journal | vauthors = Gustafsson A, Lindenfors P | title = Human size evolution: no evolutionary allometric relationship between male and female stature | journal = Journal of Human Evolution | volume = 47 | issue = 4 | pages = 253–266 | date = October 2004 | pmid = 15454336 | doi = 10.1016/j.jhevol.2004.07.004 }}</ref><ref name="NHANES_III_data">{{cite journal | vauthors = Ogden CL, Fryar CD, Carroll MD, Flegal KM | title = Mean body weight, height, and body mass index, United States 1960–2002 | journal = Advance Data | volume = | issue = 347 | pages = 1–17 | date = October 2004 | pmid = 15544194 | doi = | url = https://www.cdc.gov/nchs/data/ad/ad347.pdf | archive-url = https://archive.wikiwix.com/cache/20110223153209/https://www.cdc.gov/nchs/data/ad/ad347.pdf |archive-date=23 February 2011 }}</ref> On average, men have about 40–50% more upper body strength and 20–30% more lower body strength than women at the same weight, due to higher amounts of muscle and larger muscle fibers.<ref>{{cite journal | vauthors = Miller AE, MacDougall JD, Tarnopolsky MA, Sale DG | title = Gender differences in strength and muscle fiber characteristics | journal = European Journal of Applied Physiology and Occupational Physiology | volume = 66 | issue = 3 | pages = 254–262 | year = 1993 | pmid = 8477683 | doi = 10.1007/BF00235103 | hdl-access = free | s2cid = 206772211 | hdl = 11375/22586 }}</ref> Women generally have a higher [[body fat]] percentage than men.<ref>{{Cite book | vauthors = Bredella MA |chapter=Sex Differences in Body Composition|date=2017 |title=Sex and Gender Factors Affecting Metabolic Homeostasis, Diabetes and Obesity |series=Advances in Experimental Medicine and Biology|volume=1043 |pages=9–27| veditors = Mauvais-Jarvis F |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-319-70178-3_2 |pmid=29224088|isbn=978-3-319-70177-6 }}</ref> Women have [[Human skin color#Sexual dimorphism|lighter skin]] than men of the same population; this has been explained by a higher need for vitamin D in females during pregnancy and [[lactation]].<ref>{{cite journal | vauthors = Rahrovan S, Fanian F, Mehryan P, Humbert P, Firooz A | title = Male versus female skin: What dermatologists and cosmeticians should know | journal = International Journal of Women's Dermatology | volume = 4 | issue = 3 | pages = 122–130 | date = September 2018 | pmid = 30175213 | pmc = 6116811 | doi = 10.1016/j.ijwd.2018.03.002 }}</ref> As there are chromosomal differences between females and males, some X and Y chromosome-related conditions and [[Disease|disorders]] only affect either men or women.<ref>{{cite web|vauthors=Easter C|title=Sex Linked|url=https://www.genome.gov/genetics-glossary/Sex-Linked|access-date=18 April 2021|website=National Human Genome Research Institute|language=en|archive-date=14 April 2022|archive-url=https://web.archive.org/web/20220414183337/https://www.genome.gov/genetics-glossary/Sex-Linked|url-status=live}}</ref> After allowing for body weight and volume, the male voice is usually an [[octave]] deeper than the female voice.<ref>{{cite journal | vauthors = Puts DA, Gaulin SJ, Verdolini K | title = Dominance and the evolution of sexual dimorphism in human voice pitch. | journal = Evolution and Human Behavior | date = July 2006 | volume = 27 | issue = 4 | pages = 283–296 | doi = 10.1016/j.evolhumbehav.2005.11.003 | s2cid = 32562654 }}</ref> Women have a [[Sex differences in longevity|longer life span]] in almost every population around the world.<ref name="WHO">{{cite web | url = https://www.who.int/gender/documents/en/ | title = Gender, women, and health | archive-url = https://web.archive.org/web/20130625083240/https://www.who.int/gender/documents/en/ | archive-date=25 June 2013 | work = Reports from WHO 2002–2005 }}</ref> There are [[intersex]] conditions in the human population, however these are rare.<ref>{{Cite journal |last=Sax |first=Leonard |date=1 August 2002 |title=How common is lntersex? A response to Anne Fausto-Sterling |url=https://www.tandfonline.com/doi/full/10.1080/00224490209552139 |journal=The Journal of Sex Research |language=en |volume=39 |issue=3 |pages=174–178 |doi=10.1080/00224490209552139 |pmid=12476264 |s2cid=33795209 |issn=0022-4499}}</ref>